Physics Nobels go to cat herders (Schrödinger’s cat, that is)

Nobels reward "measuring and manipulating single quantum systems."

This year's Nobel Prize in Physics goes to a pair of physicists that pioneered experimental approaches to the quantum world. The two, University of Colorado-Boulder's David Wineland and Serge Haroche from the Collège de France, used coupled systems of single atoms and photons to provide ways of monitoring a quantum object without destroying its quantum nature. Like any good quantum experiment, there are multiple ways of looking at what they've done, but the Prize announcement highlights the fact that their work is already having practical applications, as it's being put to use in ultra-high-precision atomic clocks and attempts to build quantum computers.

Classical physics, which governs the everyday world of the objects around us, is deterministic; an object is either in a given state, or it's not. But quantum systems are probabilistic, with their objects only having certain odds of being in different states. And until that state is determined, the objects actually behave as if they are in all possible states. That's why a single photon can behave as if it travels through two paths at once, creating an interference pattern with itself.

This is most famously thought of in terms of Schrödinger's cat, in which the cat's life is dependent upon the state of a quantum system. As long as the cat is in the box, we can't know whether it's alive or dead. From a quantum perspective, the cat is in a superposition of both alive and dead. The cat also demonstrates other aspects of the quantum system. For example, by measuring its state—opening the box and looking at the cat—we typically destroy its quantum nature. And it shows that there's some poorly defined boundary between the quantum and classical worlds. No matter how we set up the experiment, the cat will always be classical, either alive or dead.

But for decades after Schrödinger first described it, cat-like states were purely hypothetical. We actually couldn't create and measure a well-defined quantum system. Wineland and Haroche are being honored for developing the systems that changed that.

Both of them worked with a kind of trap that held an individual object. In Wineland's case, his work took advantage of the development of ion traps, which held individual ions at temperatures near absolute zero, where they could be probed with lasers. Haroche did things the opposite way around, creating a trap for a single photon using highly reflective mirrors that are spaced at distances shorter than the photon's wavelength. To probe the state of the photon, researchers can slide specially prepared atoms (called Rydberg atoms) through the trap, which change state based on the presence or absence of the photon.

(The Nobel announcement highlights an impressive fact about these optical traps. Even though the mirrors are only 2.7cm apart, a typical photon will manage to travel about 40,000km between them before being lost).

The resulting systems have allowed the researchers to study quantum entanglement, observe the system as measurements destroy its quantum state, and study how its interactions with its environment gradually cause the quantum system to return to a classical state.

As is often the case, these systems weren't developed in isolation. Ion traps had been around for roughly a decade before Wineland figured out how to set the ions in one into the lowest energy ground state. In another case, other researchers proposed a theoretical method for transferring quantum states within an ion trap; Wineland's group published their implementation of it later that same year. Haroche's group did much the same thing the year afterwards, when his own group first proposed, then generated a system for creating and observing the decay of a cat-like system—all in under a year.

Neither group has sat still since these accomplishments. Haroche has helped develop systems where equipment can provide real-time feedback to a quantum state, delaying its decay into a classical system. Depending on the route eventually taken to quantum computing, this sort of system may be essential for stabilizing the qubits. Meanwhile, Wineland has been using his systems to develop atomic clocks that enable staggeringly precise time measurements. "The accuracy recently achieved by the optical clocks has allowed Wineland and coworkers to measure relativistic effects," the Nobel's press material states "such as time dilation at speeds of a few kilometers per hour or the difference in gravitational potential between two points with a height difference of only about 30cm."

Perhaps the greatest tribute to the work of the researchers, however, is how commonplace this has all become. Skimming through the latest papers in physics and optics shows that the study of single quantum objects goes on in hundreds of labs around the globe now. It makes it hard to imagine that, only a few decades before, it was an important breakthrough.

if you define the cat as its accumulative collection of particles in their various quantum states, does it still hold true the cat is classical?

Yes, the cat is still classical because the various sub-atomic particles are also classical when observed, i.e. the act of observation collapses the superposition of states and you only observe the particle as being in one state.

If they can measure the state of a quantum without disentangling it, then they can build a communication device that can send a message faster than the speed of light. Of course, they will have to overcome this nonsense about time having a dimension, which means it won't happen any time soon.

First of all, the cat is not in a box. It's in a hat. Don't you know your Dr. Seuss? And being in a hat you can observe it just by looking down from the top of the hat. Assuming the hat is upside down of course. But if it's upside down why wouldn't the cat just jump out of it?

creating a trap for a single photon using highly reflective mirrors that are spaced at distances shorter than the photon's wavelength.

Quote:

Even though the mirrors are only 2.7cm apart, a typical photon will manage to travel about 40,000km between them before being lost

Is anyone able to help me decipher this? My understanding is that light is measured with wavelengths in the nm scale, so I get lost trying to reconcile "mirrors that are spaced at distances shorter than the photon's wavelength" with "2.7cm apart" (as if distances shorter than a wavelength weren't troublesome enough given that is a limiting factor with chip production technologies). Is "photon's wavelength" a term of art?

creating a trap for a single photon using highly reflective mirrors that are spaced at distances shorter than the photon's wavelength.

Quote:

Even though the mirrors are only 2.7cm apart, a typical photon will manage to travel about 40,000km between them before being lost

Is anyone able to help me decipher this? My understanding is that light is measured with wavelengths in the nm scale, so I get lost trying to reconcile "mirrors that are spaced at distances shorter than the photon's wavelength" with "2.7cm apart" (as if distances shorter than a wavelength weren't troublesome enough given that is a limiting factor with chip production technologies). Is "photon's wavelength" a term of art?

The wavelengths of visible light are from roughly 400-750 nm, but a photon isn't restricted to visible light. It's the electromagnetic spectrum, after all. A wavelength of 2.7 cm corresponds to a microwave, roughly 1 mm - 1 m, although the boundaries are by their nature pretty arbitrary.

"I get lost trying to reconcile "mirrors that are spaced at distances shorter than the photon's wavelength" with "2.7cm apart""

"Photon" does not necessarily imply "visible wavelength". Radio waves represent photons too, as do gamma rays, etc. In this case, it would be a low-energy photon (microwave band) with a wavelength > 2.7cm, frequency < 11GHz or so, if I got the decimal point right.

Check out http://en.wikipedia.org/wiki/Radio ; the table under the subhead "Radio Band" on that page should give some feel for how light relates to the other manifestations.

creating a trap for a single photon using highly reflective mirrors that are spaced at distances shorter than the photon's wavelength.

Quote:

Even though the mirrors are only 2.7cm apart, a typical photon will manage to travel about 40,000km between them before being lost

Is anyone able to help me decipher this? My understanding is that light is measured with wavelengths in the nm scale, so I get lost trying to reconcile "mirrors that are spaced at distances shorter than the photon's wavelength" with "2.7cm apart" (as if distances shorter than a wavelength weren't troublesome enough given that is a limiting factor with chip production technologies). Is "photon's wavelength" a term of art?

The wavelengths of visible light are from roughly 400-750 nm, but a photon isn't restricted to visible light. It's the electromagnetic spectrum, after all. A wavelength of 2.7 cm corresponds to a microwave, roughly 1 mm - 1 m, although the boundaries are by their nature pretty arbitrary.

Thank you for clearing that up. I'd never heard "photon" used outside the context of visible light, so without any reason to I assumed it must be something special in this case. What an interesting world we live in.

So a cardboard can get this guy a Nobel prize. I'll give it a bit of respect when the next time I pick up a cardboard box. Didn't know these things had been put in good use. LOL!

OTOH, as a scientist who didn't know back then nothing about a good insulation would be aluminium foil or lead. That must be came much later after so many lost lives from radiation infections. Röntgen had no idea if he had his wife sticks her hands behind the screen a few more times she ended up with bone cancer. But that's how people learn, right? Thanks for the link.

So a cardboard can get this guy a Nobel prize. I'll give it a bit of respect when the next time I pick up a cardboard box. Didn't know these things had been put in good use. LOL!

OTOH, as a scientist who didn't know back then nothing about a good insulation would be aluminium foil or lead. That must be came much later after so many lost lives from radiation infections. Röntgen had no idea if he had his wife sticks her hands behind the screen a few more times she ended up with bone cancer. But that's how people learn, right? Thanks for the link.

500 years from now those average high school students would be able to conducted the same experiments as David Wineland and Serge Haroche doing today in their own garage basements in an afternoon break. And looking back at their history reference materials and chuckles...

"Man, it's a piece of cake, Quantum, Dark matters, Black holes, just knowing how to spreading a single photon going in two directions will get them a Nobel Prize? I can spread a photon in ten million directions. Those people were so dumb, they must had suffered severely malnutrition in those days or what?"

On a slightly unrelated note, there's something I never understood about the cat paradox.If the cat's life is dependent on a quantum state of a particle that is in the box with him (by some hypothetical mechanism connecting the two), doesn't that mean a measurement is already taking place inside the box?